In a typical radio communications system, user communications radio terminals, often referred to as user equipment units (UEs), communicate via a radio access network (RAN) with other networks like the Internet. The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, which in some networks is also called a “NodeB” or an enhanced Node B. A cell is a geographical area where radio coverage is provided by radio base station equipment at a base station site.
Third Generation (3G) cellular radio systems like Universal Mobile Telecommunications System (UMTS) operating in Wideband Code Division Multiple Access (WCDMA) use different types of radio channels including circuit-switched radio channels and packet-switched radio channels. Mixed voice/data, circuit/packet switched 3G systems evolved from voice-centric, circuit-switched second generation (2G) systems. Circuit-switched channels, sometimes called dedicated channels, are usually allocated to only one user for the duration of a connection carrying information only associated with that one user. Packet-switched channels are shared, scheduled channels over which packets for multiple user connections are carried. Fourth generation (4G), OFDMA-based systems, like the Long Term Evolution (LTE) of UMTS and Worldwide Interoperability for Microwave Access (WiMAX), use an air interface design based on packet data. Dedicated traffic channels are eschewed in favor of shared radio resources in order to unify the system's ability to handle differing traffic characteristics. Medium access control is migrating towards a paradigm where user devices request resources from a base station resource scheduler which grants available radio resources to such requests in accordance with a schedule. In response to actual requests to transmit data from and/or to a user equipment (UE) in the uplink and/or the downlink, the scheduler in the base station dynamically allocates radio resources to satisfy the quality of service requirements associated with the type of data traffic to be transmitted, and at the same time, tries to optimize the system capacity.
The IEEE 802.16 Working Group on Broadband Wireless Access Standards develops formal specifications for the global deployment of broadband Wireless Metropolitan Area Networks (MAN). Although the 802.16 family of standards is officially called WirelessMAN, it is often referred to as WiMAX. WiMAX/IEEE 802.16e uses scalable orthogonal frequency division multiple access (OFDMA) to support large channel bandwidths, e.g., between 1.25 MHz and 20 MHz with up to 2048 sub-carriers. Another important physical layer feature is support for multiple-in-multiple-out (MIMO) antennas in order to provide good performance in NLOS (non-line-of-sight) conditions (or higher bandwidth). Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The performance is improved if the transmitter and the receiver use multiple antennas resulting in a multiple-input multiple-output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO.
The general problem addressed in this application is how to best design a new higher bandwidth communications system so that it is backward compatible with an existing communications system with lower signal bandwidth. For an OFDMA-based example in the IEEE 802.16 set of standards, a new standard, IEEE 802.16m, must be backward compatible with an existing IEEE 802.16e standard, as further specified by the WiMAX Forum System Profiles, which is the WirelessMAN-OFDMA reference system. Although IEEE 802.16m will operate at higher data rates than what is currently supported by the WirelessMAN-OFDMA reference system, with channel bandwidths up to 20 MHz, it is desirable for the IEEE 802.16m system to support IEEE 802.16e communications that use only 5 or 10 MHz channels For ease of reference, abbreviated forms of 802.16e/16e and 802.16m/16m are used below.